Protein tyrosine phosphatases (PTPases) are a large family of diverse molecules that can play an important role in modulating a wide variety of cellular responses. The PTPase family is divided into three major subclasses, classical PTPases, low molecular weight PTPases, and dual specificity PTPases. The classical PTPases can be further categorized into two classes, intracellular PTPases (e.g., PTP1B, TC-PTP, rat-brain PTPase, STEP, PTPMEG1, PTPH1, PTPD1, PTPD2, FAP-1/BAS, PTP1C/SH-PTP1/SHP-1 and PTP1D/Syp/SH-PTP2/SHP2) and receptor-type PTPases (e.g., CD45, LAR, PTPα, PTPβ, PTPδ, PTPε, PTPγ, SAP-1 and DEP-1). Dual specificity phosphatases have the ability to remove the phosphate group from both serine/threonine and tyrosine residues. Members of the PTPase family have been implicated as important modulators or regulators of a wide variety of cellular processes including insulin signaling, leptin signaling, T-cell activation and T-cell mediated signaling cascade, the growth of fibroblasts, platelet aggregation, and regulation of osteoblast proliferation.